Plastic container systems with caps, lids, and corks, are widely known in consumer goods and products. Unfortunately, because plastics typically have an extremely slow rate of decomposition, such plastics must be either recycled through costly industrial processes, or otherwise tossed into landfills where they will remain for centuries.
In an attempt to provide a more degradable closure system, the use of plastics such as polylactic acid polymers (PLA) have become more commonplace. However, such plastics still require specialized processes and facilities for degradation, which requires significant costs for its decomposition. In addition, PLA and similar plastics are visibly indistinguishable from normal plastics. This can be problematic because if the PLA is inadvertently placed within a group of traditional plastics to be recycled, the PLA can interfere with the normal recycling process.
Existing biodegradable closure systems are very limited; currently only non-threaded over-caps, pressure fitted discs and corks are used on consumer products. For example, WIPO Publication No. 2007/140538 to Henderson, et al. (publ. December 2007) discusses a biodegradable container and a biodegradable closure that can take the form of a plug, a membrane, or a seal. However, the Henderson closure typically cannot reseal the container once removed.
Such existing biodegradable closures have substantial shortcomings in providing a secure reusable closure that does not unduly stress a fiber-based container. For example, non-threaded over-caps and pressure fitted discs do not provide a secure positive closure. Furthermore, even though corks provide positive closure, when pressed into an opening they exert large outward forces on the opening and can weaken or crack the mouth of a fiber-based container. An alternative closure could be a threaded molded fibrous cap or lid that mates with threads on a container. Unfortunately, the threads on the closure and container would be relatively soft and likely to shear off when closed with the amount of force used by an average person. If a stiffening agent is infused in the fibrous pulp in order to strengthen the threads, the biodegradable qualities of the material are diminished.
UK Patent No. 2238270 to Hwang teaches a biodegradable lid for a beverage cup that is made of natural rubber latex. While the lid provides an effective reusable seal, various drawbacks remain. Specifically, the seal is achieved by stretching the lid over a container opening. This can put a significant amount of compressive force on the container. When the container is made of a biodegradable fibrous material, these compressive forces can easily distort or bend the container's body. On the other hand, if the lid is configured to not substantially apply a compressive force to the container, the seal is compromised and the lid may slip off
U.S. Pat. No. 5,249,549 to Rockaitis discusses a disposable pet litter container having a lid that can be removed from and reinserted into a groove in the container to thereby seal the container. Although the lid and container can be composed of biodegradable materials, the lid is configured to be removed and reinserted into the container once. Repeated removal and reinsertion of the lid into the container would likely cause the lid to be deformed.
Thus, there is still a need for a reusable biodegradable closure system with an effective seal.